1. Field of the Invention
The present invention generally relates to recording information in the form of color bands on documents, and more particularly to a thermal printer in which color coded bands are recorded on the thermally sensitive coating on the document.
2. Description of the Prior Art
Airline boarding documents are today commonly printed on a thermally sensitive surface by means of a thermal printing head. The boarding document, which is made of a relatively stiff paper stock, is transported at a relatively high speed past the printing head. The thermal printing head prints monochromatic (usually black) characters on the relatively white thermally responsive surface.
While altogether satisfactory for printing alphanumeric information on the boarding document, a thermal print head is not readily adaptable for printing color bands on the boarding document. Such bands are desirable to readily indicate a class of service for which the boarding pass is valid; i.e., first class, business class, and tourist class.
The thermally sensitive surface of the boarding document is relatively impervious and does not accept ink readily. Prior art attempts to print color stripes on the document as it is transported past the thermal print head resulted in unacceptable smearing. Further, it will be appreciated that the color striping ink must flow on command substantially instantaneously, but intermittently, which presents further problems, including clogging.